1. Field of the Invention
The present invention relates to a motor operated valve driven by a stepping motor.
2. Description of the Related Art
A refrigeration cycle in an automotive air conditioner generally includes a compressor for compressing circulating refrigerant, a condenser for condensing the compressed refrigerant, an expansion valve for throttling and expanding the condensed liquid refrigerant and delivering the resulting spray of gas-liquid mixture refrigerant, and an evaporator for evaporating the misty refrigerant and cooling the air in a vehicle interior by evaporative latent heat. For the expansion valves, mechanical expansion valves have been widely used. Such a mechanical expansion valve senses the temperature and the pressure of refrigerant at an outlet side of the evaporator and autonomously opens and closes a valve section thereof. Alternatively, motor operated valves have also been increasingly used with the recent widespread use of electric vehicles and hybrid vehicles. Motor operate valves achieve accurate control of the valve opening degree by means of stepping motors as drive units.
Such a motor operated valve converts rotational movement of a rotor into translational movement of a shaft to drive a valve element. The valve element is supported by an end of the shaft, and opens and closes the valve section by leaving and touching a valve seat formed in a refrigerant passage. To absorb the impact of the valve element touching the valve seat, the valve element is supported by the shaft in a relatively displaceable manner. Specifically, the shaft has a hollow end portion, and the valve element is partially inserted in the hollow end portion and slidably supported thereby. A spring for biasing the valve element in a valve closing direction, that is, in a direction in which the valve element is made to protrude from the shaft is disposed in an internal space of the shaft. When the valve element touches the valve seat, the spring elastically deforms to absorb the impact.
In order to control the valve opening degree of such a motor operated valve with high accuracy by means of a stepping motor, a reference position is set for defining the rotating position of the rotor. For example, a stator and the rotor are positioned so that the magnetic poles of the stator and those of the rotor are opposite to each other in a valve closed state. With this structure, when power supply is cut off in the valve closed state, the rotor is stopped at the reference position. When power supply is resumed, the valve opening degree is controlled on the basis of the reference position.
One example of valves proposed to achieve such positioning is provided with a fitting structure for positioning between a can, which is part of a motor operated valve, and a bracket attached to a stator (refer to Japanese Patent Application Publication No. 2001-304445, for example). Another example of such valves is provided with a rotation restricting member at a specific position of the stator, and achieves positioning by connecting the rotation restricting member to a pipe connected to a body (refer to Japanese Patent Application Publication No. 2005-90571, for example). These configurations may reduce bounce-back phenomena caused by misalignment of magnetic poles while the valve is being closed, for example, and may achieve stable stop of the rotor at a reference position (refer to Japanese Patent Application Publication No. 2004-357409, for example).